Electronic time division channel scanning system



. Sept. 5, 1950 l H, J, KOCH 2,521,229

ELECTRONIC TIME DIVISION CHANNEL SCANNING SYSTEM lFiled June 8, 1949 2Sheets-Sheet 1 4FIG. 2.

ATTO NEY Sept. 5, 1950 H. J. KOCH 2,521,229

ELECTRONIC TIME DIVISION CHANNEL SCANNING SYSTEM Filed June 8, 1949 2Sheets-Sheet 2 SIX PHASE POTE/VT/AL SUI/RCE FIG. 4

51X A)DH/45E POTENTIAL 50i/RCE FIG. 3

INVENTOR. r3 HENRY KOCH ATTORNEY Patented Sept. 5, 1950 UNITED STATESPATENT OFFICE ELECTRONIC TIIVIE DIVISION CHANNEL SCANNING SYSTEMApplication June s, 1949, serial No. 97,792

9 Claims. (Cl. 179-15) This invention relates to communication systemsof the multiplex kind, and more especially to multiplex systems of thepulsed channel type.

A principal object of the invention is to provide a simplified andeflcient channel scanning arrangement for timed division multiplextransmission.

Another object is to provide an improved pulsed multiplex transmitteremploying as the pulsed channel source an electron tube of the focussedrotary beam type. 4

Another object relates to a novel combination of rotary beam tube and asignal-controlled multi-section output tube, which tubes areinterconnected to provide timed division multiplex signals having arelatively low noise level. l

A feature of the invention relates to the combination of a rotary beamtube which acts as a multiplex channel pulse generator, a plural-sectioninverter tube, and a plural-section signalcontrolled tube, which tubesare interconnected to provide an improved timed division multiplexingtransmitter having a relatively low noise level.

A further feature relates to the novel organization, arrangement andrelative location of parts which cooperate to provide an improved andefficient timed division multiplex transmitter.

In the drawing, which shows, by way of example, one preferredembodiment:

Fig. 1 is a schematic structural and wiring potential.

of a metal sleeve having its external surface coated withelectron-emissive material. 4Concentrically surrounding the cathode 3,are six metallic screens 5-I0 which are spaced apartV to form respectiveWindows |I-I6, all the windows being of the same dimensions and beingequally spaced around the cathode 3. Each of the screen plates 5-Illalso has a central window |122 of substantially the same dimensions asthe windows II-IG. There are thus provided twelve windows of the samesize, equally spaced around the cathode 3. Surrounding the screenplates, and in radial alignment with each of the respective windows, isa corresponding anode 23-34. While the drawing shows twelve of thesewindows and anodes, it will be understood that a greater or less numbermay be employed, depending upon the number of multiplex channels to bedesired. Each of the screen plates 5-l0 is provided with a separatelead-in 357-40, which lead-ins `are cohnected to any Well-knownsix-phase source of The cathode 3 is returned to ground through asuitable bias resistor 2l. 'I'he anode plates are likewise connectedthrough respective lead-ins 4I, 42, 43, etc. and through respective loadresistors 44, 45, 46, etc., and thence in parallel to the positiveterminal 41 of a suitable source of plate potential representedschematically by the battery 48. As explained in said application,

diagram of a multiplex pulsed transmitter according to the invention.

Fig. 2 is a series of pulse graphs explanatory of the operation of Fig.1.

Fig. 3 is a schematic structural and wiring diagram of a multiplexreceiver according to the in-i' vention.

Fig. 4 is a modification of Fig. 1.

Referring to Fig. 1, the numeral I represents schematically a tube ofthe focussed rotary beam type. For a detailed description of such atube, reference may be had to Proceedings of the I. R. E., vol. 36, No.11, November 1948, pages 1354-1357. The tube comprises a suitable evacu-.ated enclosing envelope 2 containing a central electron-emittingcathode 3, provided with the usual internal and electrically-insulatedheater lament or element 4. The cathode 3 maybe of the type well-knownin so-called indirectlyheated cathode tubes, for example in the form bychoosing the proper bias for the cathode 3 and for the various plates,the electron beam from the cathode is focussed into a substantiallyplanar beam 49 whose transverse width is equal to'or less than thetransverse distance between the centers of the windows |I-22. saidpublication, the beam 49 is rotated synchronously at a predeterminedrate controlledby the six-phase potential source connected to the screenplates 5-10. Therefore this beam successively completes a circuitthrough each of the twelve respective resistors 44, 45, 46, etc.Consequently as the beam rotates, it develops across the respectiveresistors, negative pulses 50, 5l, 52, i Thus the pulses are spacedapart .o

etc. (Fig. 2). in time by a regular interval "t, and the recurrence timeT is equal to Nt, where N is the total number of anodes.

The pulses developed across the resistors 44, 45, 46, etc., are appliedthrough respective coupling condensers 53, 54, 55, etc., to the respec-As explained in with each -one of said windows.

current characteristic curve.

tive control grids 56, 51, 58, etc. of another tube 59. This tube can bestructurally substantially the same as that of tube I, except that allthe screen plates are electrically connected together and to the samepositive potential 60. In other words, the electrons from the cathode 6|are not focussed into a planar beam, so that they are emittedsimultaneously in all radial directions through the respective twelvewindows 62, 63, 64, etc. of the screen plates. The central cathode 6|can `.beiconnecteddirectly -.to ,ground and is surroundedlby a 1;positively chargedgrid 65 7which acts as a space charge grid for thetube by being connected to a suitable positive direct current biassingsource 66. In alignment with each of the grids 58, 51, 58, etc., :arethe respective output anodes 61, 68, 69, etc., which nare Vcon- CTInected to the positive directcurrentsupply terminal 41 throughrespective load-resistors 31.0, 12|, 12, etc. The potential of thenegative pulses 50,

5|, 52, etc. are such that when .they .are im pressed upon therespective gr'ds'56, 51, '58. etc., they out off plate current flow fromthe'fcathode 6| to the respective ariodes 61, 68, 69, etc. Thus .thenegative pulses are .converted -into Apositive r pulses-acrosstherespective .resistors .10, 1| ,`.12, ctc. These positive `.pulses.are .applied through .respective .coupling condensers 13, .14, 15,etc., to .respectiveiswitching controlgrids L16, 11, .10, etc., -.to.another tube 1.9. This tube may comprise lan.evacuated .envelope 80containing a ,central .electron-emitting .cathode 8| which is surrounded,bya ,positively-charged.-spacefcharge ,-grid l82 sup- ;pliediby'asuitable Ypositive direct currentibias- .-'singpotentialiromthe sourcel83. .Concentrically :surrounding the .grid .82 are the .screen platesssimilar to the lplates \.5|.0 of -tube vI, -but .with :all .the'.plates electrically-connected togetherfand @to these-mepositiverdirect current potential84. Thus there aretwelve windows85,185, I181etc., #equally spaced-around thecathode 8|, the grids 16,1.11, ,18, etc., being in .alignment .respectively Also concen-`.trically :surrounding Ythe 'cathode in alignment withthe saidwindowsandlocatedfbetween ,these windows 'and -the switching grids, is asimilarfseriesof signal input controlgrids 88,-89, 90, etc.

asingleoutput anode y9| concentrically surrounds fall the i-electrodes,.and is connected y=to vthe posi- `tive terminal -41 of the.directrcurrentfpower., supnply through a single -.plate loadfresistorf9.2, and thence to a common output terminal .93 -which may leadtoasuitabletransmisson line or channel. All the switchinggrids 16,:11,118, etc., are kconnected through respective grid-leak .resistors.94, 95,l *96,fetc., to thefnegative .terminal .91..of a`suitable-direct :current-biassing source 98, so .as normally tobias theswitching grids 19, 11, .18, -etc to plate'current'cutoff. =Each;ofthesignal --input grids 8.8, 89, .9.0, etc., is connected through aysuitable coupling condenser 99, |00, IDI, etc., `torespective signalinput-channels |03, |04, |05, etc. These signal inputgrids are'biassedthrough respective grid-leak resistors I 06, |01, |08, etc., ytoasuitablenegative potential 109 to maintain theyarious sectionsofthetube operating=on the zstraight .line portion-of their controlgrid-plate From the -foregoingidescription .it vwill be seen y.that theytube I ,generates regularly recurrent ,and -spaced negative pulseswhich when .applied to the tube 59, .produceat the grids 16, .1.1, 18,'.etc., correspond- ,ing,positive lpulses. .However the amplitude of.these positive pulses-can befchosen with respect to the negative biason the grids'88, 89, 90, etc.,

so that plate current does not ilow from the cathode 8| to the anode 9|except upon the timed coincidence of a positive pulse applied to aswitching grid, and a positive signal pulse applied to the correspondingsignal input grid from the respective signalling channel. On the otherhand, the magnitude of the positive pulses applied to the switchinggrids can be proportioned with respect to the negative bias on thesignal grids, so that the signal potentials applied from `the respective.channels L03, |04, .|05, etc., cause a 'modulation or the :platecurnentfflowing from the cathode 8| to the anode 9| respectively rthrough thesuccessively switched-in sections of the tube.

VFIthas-'b'eeniound that by this particular combination of tubes, andthe particular manner of Agenerating the .switching or timing pulses by.means-,of .airotary beam tube which is separate .LEO :from the channeloutput tube 19, a considerable .reduction in signal-to-noise ratio isobtained in 'the output signals at terminal 93. It will be understood,of course, that at the receiver any wellknown channel distributor can beprovided for .connecting .the various receiving channels .into

circuit, with Vterminal 93 in Ytimed .coincidence with .theimpingementof the 'electron .beam .'49 on thesuccessiveanodes23434. Preferably thisdistributor may comprise a rotary beam tube IIO (seeFig. 3), similar totube I, havingits 'focussed electron beam rotating in timed synchronismwith .the beam 4.9. Thus this tube may comprise a centralelectron-emitting cathode I'I which is surrounded bythe six screenYplates I I2, |`|'3, '|4, etc., to provide a series of twelveequally-'spaced windows `I I5, II6, I|1, etc., similar to the twelvewindows in the screenplate of tube 'I. vThesesix screen plates are thenconnectedto 'a suitable .sixfphase .alternating .current source whichjis synchronized with the six-,phase alternating 'current source at thetransmitter. Concentrically surrounding the twelve windows is aunipoten- .tialgrid I 8 which is connected to the transmission channel9-3. Concentrically surrounding the cathode, and in alignment with the'twelve windows in the screen plates, are twelve output anodes I9, .|20,112|, etc., which are connected through respective load Aresistors |22,|23, 124, etc., and thence through respective coupling con- .densers|25, |26, |21, etc., to the respectivereceiving channels |28, |29, |30,etc. The output anodes ||9, |20, 2|, etc., are connected through theirrespective load resistors |22, |23, "|24, etc., tothe positive terminalylill of the direct current plate power supply |32. The grid |I8 can bevbiassed negatively by a suitable direct current supply |33, so that apulse ofplate current does not ow to the respective output anodesV'except upon the receipt of a positivepulsereceivedirom the.transmission channel'93, andyif desired, the magnitude of this pulse ofplate current can "be in proportion to themodulation or amplitude of thereceived positive pulse.

Eig. '4 shows a modification o'f the .system of Fig. '1, whereby thetube A59 :can be eliminated,

55 The slat electrodes` |1`22 vare connected to a suitablesix-phasesource, and the cathode 3 is biassed -with respect to the remainingelectrodes, to cause the focussed planar beam 49`to rotate at therequiredrate. Located between the slat electrodes Y ,and .the anodes, isa cylindrical mesh grid |34 which is connected to a positivel terminal|35 of .ethe direct current plate power supply source |36.

The anodes 23, 24, 25, are connected through their respective loadresistors 44, 45, 46, etc., to another tap |31 on the supply |36. Thusthe anodes are at a lower positive potential than the electron collectorgrid |34. Consequently as the beam 49 rotates, it impinges successivelyupon the anodes and produces positive pulses at these anodes, and thesepositive pulses can be coupled through the condensers 53, 54, 55, etc.,to control the tube 19 in the manner above de scribed.

While certain particular embodiments have been disclosed herein, variouschanges and modications may be made therein without departing from thespirit and scope of the invention.

What is claimed is:

1. A multiplex communication system, comprising, an electron tube havinga central electron-emitting cathode, a plurality of separate anodesconcentrically surrounding the cathode, means to develop the electronsfrom the cathode into a beam originating at the cathode and terminatingsuccessively at said anodes, means to develop a beam-rotating iield tocause said beam to sweep said anodes to develop regularly recurrentpulses at said anodes successively, means to derive from said regularlyrecurrent pulses another set of switching control pulses synchronizedtherewith another electron tube having a central electron-emittingcathode and a surrounding anode, a rst set of separate grids surroundingthe cathode of said other tube, a second set of separate grids in saidother` tube and surrounding the first Iset of grids and in radialalignment therewith, a plurality of signal input channels connectedrespectively to the grids of the first set, a single output channelconnected to said anode of said second tube and means to apply saidderived pulses respectively and recurrently to said second sets of gridsto control successively the conductivity between each grid of the firstset and said single anode.

2. A multiplex communication system according to claim 1, in which theelectrons from the cathode of the first-mentioned tube areelectrostatically focussed to produce a beam which extends radially inone direction only from the cathode to each of said anodes insuccession.

3. A multiplex communication system according to claim 1, in which themeans to develop the said beam of electrons and the means to rotate saidbeam, comprises, a plurality of slat electrodes located between thecathode and the anodes with the slat spaces aligned each with arespective anode, and a source of multi-phase potential connected tosaid slat electrodes to develop a rotating electric eld.

4. A multiplex communication system according to claim 1, in which athird electron tube is provided having a central electron-emittingcathode with a plurality of spaced surrounding grids and a plurality ofspaced surrounding anodes, means connecting each of the grids of saidthird tube respectively to the anodes of the first-mentioned tube, andmeans connecting the anodes of said third tube respectively to thesecondmentioned grids of said other tube.

...6 5. A multiplexcommunication system of the pulse transmission type,comprising', an electron tube of the rotary beamtype having a pluralityof output anodes fordeveloping'regularly recurrent spaced pulses inresponse to the sweeping of said anodes byN said beam, a pulsel'inverter tube having a plurality of control grids and a correspondingplurality of output anodes for inverting the polarity of said pulses,and a switching and signal control tube having av plurality of signalinput grids connected respectively to a series of signal input channels,a corresponding series of switching grids connected respectively to theanodes of said inverter tube, and a signal output channel connected tothe anode of said switching and signal control tube.

6. A multiplex communication system according to claim 1, in which thefirst-mentioned tube has its anodes provided with a coating of secondaryelectron-emissive material facing the cathode, and means are providedfor causing positive pulses to be produced at said anodes in response tothe rotation of said beam past each anode.

7. Multiplex communication apparatus, comprising, a rst electron tube ofthe type having a central electron-emitting cathode and a plurality ofsurrounding spaced anodes, means to focus the beam from said cathodeinto a substantially flat beam with one edge extending along the cathodeand the opposite edge terminating at one of said anodes, means tosubject said beam to an electric field to cause it to rotate at apredetermined rate and thereby to generate recurrent pulses successivelyat said anodes, a second electron tube having a central electronemittingcathode, a plurality of spaced signal control grids surrounding thecathode, a plurality of switching grids surrounding the control gridsand in radial alignment therewith, a single anode surrounding theswitching grids, means connecting a plurality of signalling channelsrespectively to said signal control grids, means to energize saidswitching grids respectively by said recurrent pulses from the anodes ofthe iirst tube, a third electron tube having a central electron-emittingcathode, a plurality of separate anodes concentrically spaced around thecathode of said third tube, a control grid surrounding the cathode ofsaid third tube, means to focus the electrons from the cathode of saidthird tube into a substantially dat beam having one edge extending alongthe cathode and the opposite edge extending along the anode of saidthird tube, means to subject th-e beam of said third tube to an electricfield to cause it to rotate in synchronism with the beam of thefirst-mentioned tube, a signal transmission channel connecting the anodeoi' said second tube to the control grid of said `third tube, and aplurality of signal receiving channels connected respectively to theanodes of said third tube.

8. Multiplex communication apparatus according to claim 7, in which thefirst-mentioned tube develops said recurrent pulses as negative pulsesat its anodes, and a pulse inverter tube is connected between the rstand second tubes to convert said negative pulses into positive pulses.

9. Multiplex communication apparatus according to claim 8, in which theinverter tube comprises a central electron-emitting cathode, a pluralityof circumferentially-spaced control grids concentrically surrounding thecathode of said inverter tube, a plurality of circumferentiallyspacedanodes surrounding the cathode of said

